Epidermal sensor system and process

ABSTRACT

Epidermal electronics are sensors with mechanical properties matching human epidermis. Their manufacturing process includes photolithography and dry and wet etching within cleanroom facilities. The high cost of manpower, materials, photo masks, and facilities greatly hinders the commercialization potential of disposable epidermal electronics. In contrast, an embodiment of the invention includes a low cost, high throughput, bench top “cut-and-paste” method to complete the freeform manufacture of epidermal sensor system (ESS) in minutes. This versatile method works for many types of thin metal and polymeric sheets and is compatible with many tattoo adhesives or medical tapes. The resultant ESS is highly multimaterial and multifunctional and may measure ECG, EMG, skin temperature, skin hydration, as well as respiratory rate. Also, a stretchable planar coil made of serpentine ribbons can be used as a wireless strain gauge and/or a near field communication (NFC) antenna. Other embodiments are described herein.

PRIORITY CLAIM

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/971,945, filed Mar. 28, 2014, the content of which is herebyincorporated by reference.

FUNDING

This invention was made with government support under Grant nos.CMMI1301335, and CMMI1351875 awarded by the National Science Foundation.The government has certain rights in the invention.

TECHNICAL FIELD

Embodiments of the invention are in the field of flexible andstretchable sensors.

BACKGROUND

An animal body radiates data about itself. Wearable devices that cantransmit information from a body (e.g., animal or human) have theability to transform two prominent fields: mobile health (mHealth) andhuman-machine interface (HMI). In addition to fitness tracking, longterm tracking of physiological signals helps in the detection of heartfailure, epilepsy, and other conditions. However, wafer-basedelectronics remain intrinsically planar, rigid, and brittle. As aresult, state-of-the-art integrated circuit (IC)-based wearable devicesare in the form factors of “chips on tapes” or “bricks on straps”, whichare unable to maintain intimate and prolonged contact with a curved,soil, and dynamic human body to retrieve long-term, high-fidelityphysiological signals.

Recent advancements in flexible and stretchable electronics haveprovided viable solutions to the intimate integration of electronicswith bio-systems. Among many breakthroughs, an epidermal electronicsystem(s) represents a wearable device whose mechanical properties matchthat of human skin. As a result, an epidermal electronic system canconform to human skin like a temporary transfer tattoo and deform like anatural extension of the skin without detachment or fracture. Anepidermal electronic system may monitor electrophysiological signals,skin temperature, skin hydration, sweat, and motion disorders.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the present invention willbecome apparent from the appended claims, the following detaileddescription of one or more example embodiments, and the correspondingfigures. Where considered appropriate, reference labels have beenrepeated among the figures to indicate corresponding or analogouselements.

FIGS. 1(a)-(h) depict a process in an embodiment of the invention.

FIGS. 2(a)-(b) depict a sensor in an embodiment of the invention.

FIGS. 3(a)-(f) address strain in various embodiments of the invention.

FIGS. 4(a)-(l) include images of various embodiments of the invention.

FIGS. 5(a)-(g) include images concerning a strain gauge and antenna inan embodiment of the invention.

FIGS. 6(a)-(h) include images and analysis concerning a respiratory ratesensor in an embodiment of the invention.

FIG. 7 includes a system for use with various embodiments of theinvention.

FIG. 8 depicts a process stage in an embodiment of the invention.

FIG. 9 includes a process for forming an epidermal sensor system (ESS)in an embodiment of the invention.

FIG. 10 includes a process for forming an ESS in an embodiment of theinvention.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like structures maybe provided with like suffix reference designations. In order to showthe structures of various embodiments more clearly, the drawingsincluded herein are diagrammatic representations of sensor/circuitstructures. Thus, the actual appearance of the fabricated integratedcircuit structures, for example in a photomicrograph, may appeardifferent while still incorporating the claimed structures of theillustrated embodiments. Moreover, the drawings may only show thestructures useful to understand the illustrated embodiments. Additionalstructures known in the art may not have been included to maintain theclarity of the drawings. For example, not every layer of a semiconductordevice is necessarily shown. “An embodiment”, “various embodiments” andthe like indicate embodiment(s) so described may include particularfeatures, structures, or characteristics, but not every embodimentnecessarily includes the particular features, structures, orcharacteristics. Some embodiments may have some, all, or none of thefeatures described for other embodiments. “First”, “second”, “third” andthe like describe a common object and indicate different instances oflike objects are being referred to. Such adjectives do not imply objectsso described must be in a given sequence, either temporally, spatially,in ranking, or in any other manner. “Connected” may indicate elementsare in direct physical or electrical contact with each other and“coupled” may indicate elements co-operate or interact with each other,but they may or may not be in direct physical or electrical contact.

The thinness and softness of conventional epidermal electronic systemsleads to collapsing and crumpling of the devices after they are peeledoff human skin, making their ideal use temporary. As a result, thesuccess of epidermal electronic system technology hinges on therealization of low cost, high throughput manufacture of the devices.However, current manufacture of epidermal electronic systems relies onstandard microfabrication processes including spin coating,photolithography, wet or dry etching, and transfer-printing. Although ithas been proven effective, there are several limitations associated withsuch a process. First, the high cost associated with cleanroomfacilities, photo masks, and photolithography chemicals preventsepidermal sensors from being low cost enough to be disposable. Second,the high vacuum processes can be very time consuming and impractical forthick metal deposition. Third, the epidermal electronic system size islimited to the wafer size which has to compatible with all the vacuumchambers. Fourth, the manpower-demanding manufacturing process greatlylimits the accessibility of epidermal electronic systems to academicresearch.

In contrast, an embodiment provides a “cut-and-paste” method forcreating an “epidermal sensor system” (ESS) that offers a very simplesolution to the abovementioned challenges. Instead of performing highvacuum metal deposition, thin metal-on-polymer laminates of variousthicknesses can be directly purchased from industrial manufacturers ofshielding tapes. Instead of using photolithography patterning, a benchtop electronic cutting machine is used to mechanically carve out thedesigned ribbon shapes (or other shapes) with excess material beingremoved. This is a free-form manufacturing process that is the inverseto popular additive manufacturing technologies. Since the patterns canbe formed directly on thermal release tapes (TRT), the patterned ribbonscan be directly printed onto a variety of types of tattoo adhesives andmedical tapes without a “picking up” step (e.g., such as when apolydimethylsiloxane (PDMS) stamp is used to transfer silicon epidermalelectronic system components from a substrate). In an embodiment, somecutting machines form patterns on thin sheet metals and polymers up to12 inches wide and several feet long (while other such machines mayhandle wider or longer materials), which exceeds lab-scale wafer size(thereby increasing through put and lowering costs as compared tolithography based processes). The whole process can be completed on abench top in minutes (e.g., 10 minutes) without using a wet process(e.g., wet etching), which affords very fast training of the techniciansthat make the product and an overall easy turnaround.

As shown in embodiments described herein, multimaterial ESS arefabricated using the “cut-and-paste” technology. The resultant ESS hasbeen successfully applied to measure electrocardiogram (ECG),electromyogram (EMG), electroencephalogram (EEG), skin temperature, skinhydration, and respiratory rate. In an embodiment, planar stretchablecoils of thick aluminum ribbons are also integrated on the ESS as awireless strain gauge. The strain gauge also serves as an antenna (e.g.,NFC antenna) in some embodiments.

FIGS. 1(a)-(h) depict a process in an embodiment of the invention,including a schematic of the bench top “cut-and-paste” process. Sincepolymer-supported metal thin films are much more stretchable thanfreestanding metal sheets, an embodiment uses polymer-supported metalsheets as the starting materials. Starting materials, including goldcoated polyimide or aluminum laminated polyethylene terephthalate (PFT),can be purchased from industrial vendors. An embodiment uses thermalevaporation to deposit 100 nm gold film 102 on 13 μm transparent PFTtape 101 (FIG. 1(a), Element 905 of FIG. 9).

To manufacture gold-based stretchable electrophysiological (EP)electrodes, temperature sensors, and concentric dot-ring impedancesensors, the gold coated PFT sheet is uniformly bonded to a thermalrelease tape with the gold side facing the TRT adhesive side 103, asshown in FIG. 1(b) (see also element 910 of FIG. 9). The other side ofthe TRT 104 is adhered or placed on a cutting mat, as shown in FIG. 1(c)(see also element 910 of FIG. 9).

As seen in FIGS. 1(b)(c)(f), PET layer 101, Au layer 102, TRT adhesivelayer 103, and TRT layer 104 are all parts of long lengths of materialfed (right to left or vice versa) by rollers 113, 114, 131, 132, 133,134 or other conveyor tools known in the manufacturing arts. This is notpossible with stiff silicon wafers, photolithography tools, clean rooms,and the like.

In FIG. 1(c) the cutting mat 116 is fed into an electronic cuttingmachine (e.g., Silhouette CAMEO®, Silhouette America, Inc., West Orem,Utah, USA) with the PET side 101 facing up towards cutting tool 115(element 915 of FIG. 9). While the cutting tool may be a knife or sharpobject in some embodiments, it may be a laser or other cutting tool inother embodiments. By importing designs generated by commercial software(e.g., AutoCAD® design) into the cutting machine, the cutting machineautomatically carves the Au/PET sheets 101, 102 with customizedpatterned cuts 121, 122, 123, 124 to yield desired patterns 125, 126(FIG. 1(c) and element 920 of FIG. 9). Cutting machines are fullycapable of generating features with 200 μm resolution (although otherembodiments may have finer or greater resolution) with acceptablefeature uniformity and roughness.

Once patterns 125, 126 are formed, the TRT is removed from the cuttingmat (FIG. 1(d)) over heating element 117 at 115° C. for 1˜2 minutes (seeelement 925 of FIG. 9). In other embodiments the heating element may becoupled to the cutting tool so the composite does not need to be removedfrom the cutting tool in order to deactivate the adhesive components ofthe TRT. Exposure to the heating element deactivates the adhesive 103 onthe TRT tape so that the excessive portions 127, 128, 129 can be removedfrom the TRT (FIG. 1(d) and element 930 of FIG. 9), leaving only thedevice patterns 125, 126 loosely resting on the TRT (FIG. 1(c)). Theymay be removed by manually peeling off portions 127, 128, 129. In otherembodiments they may be removed using vacuum/pressure gradient cups 118,119, 120. In other embodiments they may be removed using patternedadhesives that align with material to be removed.

The device patterns will be printed onto a target substrate with nativeadhesives, such as skin tape 141 or a tattoo adhesive (e.g., Silhouette®temporary tattoo paper), medical tape transparent dressing (e.g., 3MTegaderm™), or 3M® type removal silicone tape (FIG. 1(c) and element 935of FIG. 9), yielding a gold-based ESS (FIG. 1(f) that is covered withliner 142 until ready for use (see element 940 of FIG. 9).

Once printed and lined, the ESS (along with other ESS printed before andafter the ESS focused upon in FIGS. 1(a)-(f)) are stored in a roll 143(FIG. 1(g)). In other words, the process in FIGS. 1(a)-(f) is repeatedin assembly line fashion creating a long strip of disposable ESS thatare easily stored, transported, and deployed from roll 143, or a foldedsheet, and the like. Individual ESS can then be removed at perforations111, 112 (see FIG. 1(h) and element 945 of FIG. 9). FIG. 1(h) includes aportion from a roll or strip of ESSs including perforated portions 111,112 around an ESS including sensors 125, 126. Additional ESS are locatedon either side of the ESS including sensors 125, 126.

In an embodiment the process in FIGS. 1(a)-(f) is repeated but withother thin sheets of metals and polymers (e.g., using Al instead of Au102 to form patterns that are formed on skin tape 141 and liner 142,such as an antenna coil or strain gauge) rendering a multimaterial,multiparametric ESS all on a final tape. In other words, the process maybe repeated to form layers of ESS systems upon one another or the ESSmay be interspersed with each other (addressed in regard to FIG. 8).

Design and Skin Integration of Multiparametric ESS

FIGS. 2(a)-(b) depict a sensor in an embodiment of the invention,including a multimaterial, multiparametric ESS printed on tattoo paper(Silhouette). In FIG. 2(a) ESS 200 includes three filamentary serpentine(FS) gold EP electrodes 228, one FS gold resistance temperature detector(RTD) 225, two dot-ring gold impedance sensors (226) that function ashydration sensors. ESS 200 also includes a planar FS coil (227) based onAl ribbons with Al facing skin tape 203, which functions as a wirelessstrain gauge and also as a NFC antenna. ESS 200 is stretchable as seenin the three pictures of FIG. 2(b). For the three FS EP electrodes 228,the inter-electrode distance 281 is set to be 2 cm for effective EPsignal recording. The FS electrodes 228 are designed with ⅕ ribbon widthto are radius to balance the trade-off between stretchability and realestate. The same design is not applicable to the Al coil 227 because thecoil would consume too much space for an ESS.

In an embodiment, coil 227 is designed by taking into accountinductance, stretchability, and overall size. The resonant frequency (f)of a RLC circuit depends on its inductance and capacitance determinedthrough the equation:

$\begin{matrix}{f = \frac{1}{2\pi \sqrt{LC}}} & (1)\end{matrix}$

in which L is the inductance and C is the capacitance. An embodimentincludes a low frequency coil that operates <100 MHz for purposes ofeasier measurement. In some embodiments, the same low frequency coil isused as an NFC coil. Equation (1) suggests the coil should have highinductance and/or capacitance to have a lower resonant frequency in anembodiment.

The capacitance of a parallel-plate capacitor is given by:

$\begin{matrix}{C = {ɛ\frac{A}{d}}} & (2)\end{matrix}$

where ε denotes the absolute permittivity of the dielectric layer, A isthe overlapped area of the parallel plates, and d is the thickness ofthe dielectric layer between the plates. There is an upper limit of thefeasible capacitance for an ESS since the area of the parallel platecannot be too large for a skin based system, the dielectric thicknesscannot be too small, and some embodiments do not include rigid chipcapacitors.

Therefore, in lieu of a large capacitance, a coil with large inductanceis used in some embodiments. Another reason it is desirable to have theresonant frequency largely set by the inductor (in some embodiments) isthat any change in strain produces a large change in the inductance.Thus, the frequency shift is more sensitive to strain. Inductancedepends on the layout of the circuit. For a planar circuit inductancedepends on the number of turns, shape of the turns, and the area that iscovered by the circuit. In general, the larger the area and the moreturns—the higher the inductance. However, this conflicts with the needof building a wireless strain gauge that is reasonably small so that itcan be properly fitted on the majority of parts of the body. Anembodiment also has a coil that is highly stretchable and compliant sothat the coil does not mechanically load the skin.

With the aforementioned coil characteristics and/or challenges in mind,an embodiment includes a double-stranded serpentine design 227 in FIG.2(a). For example, strands 261, 262 compose one double strand, strands263, 264 compose another double strand, and strands 265, 266 compose yetanother double strand. This design helps maximize the use of limitedreal estate to fill in as many serpentine-shaped turns as possible.Meanwhile it leaves reasonable gaps between serpentine portions sostretchability of the coil is ensured (FIGS. 3(a) and (b), FIG. 5(c)).Embodiments include coil 227 along the outer periphery of the ESS patchwith the coil surrounding sensors, such as ECG sensors.

The two gold “long-horns” designs at the upper left and right corners ofpatch 200 serve as alignment markers for consecutive printings ofdifferent materials on the same tape (e.g., see FIG. 8 and relateddiscussion). In an embodiment, the overall size of the device area is7.5 cm×5 cm, which is supported by a 6″×8″ large and 47 μm thick skintape 203.

The Young's module of the different polymers used in ESS vary. Tegaderm™is the most compliant of all polymers measured. Its modulus (7.4 MPa) isclose to the high end of the modulus of human skin (0.32˜4 MPa). Thestretchability of different serpentine shapes and materials were testedand modeled. Electromechanical measurement with in situ top downobservation was used to conduct the stretchability measurements. Whenelectrical resistance is measured as a function of the applied uniaxialtensile strain, the applied strain at which the resistance increasesdramatically/“explodes” is considered the strain-to-rupture orstretchability. While straight Al PET and Au PET ribbons exhibit verylimited stretchability (2.89% and 13.72%, respectively), theirserpentine counterparts are much more stretchable (all of which exceedthe elastic limit of human skin (30%)). Al serpentine patterns 227rupture at a strain of 68%, at which point failure points at theserpentine crests can be observed. The gold EP sensor 228 exploits a FSnetwork design, which ruptures at a strain of 115%, with failure pointsat strand intersections. The gold RTD sensor 225 consists ofone-dimensional dimensional (1D) FS serpentine ribbons, whichdemonstrates the largest stretchability (199%) among sensors 225, 227,228, and fracturing sites are found again at the crest of the serpentinestrands. The location of rupture can be predicted by finding the maximumprincipal strain using finite element modeling (FEM). FEM models (FIGS.3(b), (d), (f)) were created for three different serpentine strands(FIGS. 3(a), (c), (e)). While the maximum strain occurs at the crests of1D serpentines (FIGS. 3(b) and (f), FS networks are most vulnerable atthe intersections of orthogonal serpentine ribbons due to strainconcentration (FIG. 3(d)).

The interaction of ESS on different skin tapes and human skin varies.While Tegaderm™ and tattoo papers are thin, transparent, and trulyskin-like, a cloth tape (3M™ Kind Removal Silicone Tape) is muchthicker. However, although Tegaderm™ and tattoo paper are one time use,the cloth tape does not crumple after being peeled off from the skin andthe silicone adhesive allows multiple uses before losing adhesion. Theelectrical resistance of the Au and Al serpentines before and aftervarious kinds of skin deformation (stretching, compression, shear,poking, etc.) is very consistent with little to no change between“before” stretching resistance and “after” stretching resistance. It isevident that the ESS can survive most possible skin deformations thatthe skin is able to experience.

Au-Based EP, Skin temperature, and Skin Hydration Sensors

An embodiment including a multiparametric ESS has been successfullyapplied to perform real time, continuous measurements on EP, skintemperature, skin hydration, and respiratory rate. Embodiments of the Auand Al based sensors are shown in FIG. 2(a). EP signals on the surfaceof human skin pertain to the flow of ions in biological tissues andorgans, and reflect the function and health of them. For example, EEGmeasured from the surface of a human brain not only captures cognitiveand memory performance, but also reflects brain disorders like epilepsyand stroke. Noninvasive ambulatory monitoring of ECG on a human chesthelp detect an irregular heartbeat (e.g., arrhythmia). EMG measured on ahuman muscle helps identify neuromuscular diseases and can also serve asa control signal for prosthetic devices or other machines.

There are three FS EP sensors integrated on the ESS patch (collectivelylabeled 228). One acts as a reference to eliminate ground noise, and thedifferential between the other two sensors are the EP signals. The skinsurface is first lightly abrased with a paper towel to remove dead skin,then wiped down with an alcohol swab to remove any skin oils. After theskin preparation. Applicants applied one ESS (see embodiment of FIG.2(a)) and two conventional Ag/AgCl electrodes on the left chest.Simultaneously measured ECG waveforms (measured by connectingconventional Ag/AgCl gel electrodes and the ESS electrodes) were sent toan EP recorder, recorded, and processed using moving averagecalculations and DC offset compensation. The heart rate is generallyidentical from both measurements, with the ESS actually able to revealmore subtle features of ECG (e.g., better capability to sense weaksignals on the chest) than the Ag/AgCl gel electrodes.

Muscle activity is reflected by EMG. Applicant placed the same ESSembodiment (FIG. 2(a)) over the forearm (specifically on the flexormuscles) to measure EMG. Two instance of hand clenching action wererecorded via the ESS. The intensity of the gripping force was measuredby a commercial dynamometer with a higher gripping force correspondingto a larger amplitude in the measured EMG. The ESS provided reliable andaccurate measurements.

Applicant measured EEG by adhering conventional Ag/AgCl electrodes andthe ESS (FIG. 2(a)) on a human forehead with a reference FS electrodebehind the human ear. There was remarkable agreement betweenconventional and ESS measured EEG and their FFT spectrums almost fullyoverlap. Also, the spectrum of eye open and eye-closed EEG were bothmeasured by ESS. The alpha rhythm (10 Hz peak) clearly shows up when anawakened subject closes his eyes.

In addition to EP, skin temperature and skin hydration are also usefulindicators of human physiology. For example, skin temperature isassociated with cardiovascular health, cognitive state, malignancy, andthe like. Skin hydration is widely used in dermatology and cosmetologyfor the detection of diseases (e.g., eczema, atopic dermatitis, and thelike), the assessment of mental stress or hormone levels, and theevaluation of medical therapies or cosmetic treatments.

Temperature fluctuation affects the collision of electrons in metals,resulting in a change in resistance. The Resistance Temperature Detector(RTD) 225 is made of wavy serpentine gold film (100 nm in thickness) inan embodiment, which are patterned in a confined area. Due to theserpentine shape the overall length of the RTD is around 0.3 m.Applicant performed a calibration test by placing both RTD 225 and acommercial thermal couple on a hotplate at the same time and recordingthe resistance of the RTD and reading of the thermal couple while thetemperature of the hotplate was increased gradually. The resultsindicate the fractional change of the resistance is linearlyproportional to temperature, which is

$\begin{matrix}{\frac{\Delta \; R}{R} = {\alpha \mspace{11mu} \left( {T - T_{0}} \right)}} & (3)\end{matrix}$

in which α is the temperature coefficient of resistance, T is theincreased temperature, and T_(o) is the original temperature before thetemperature is increased to T, R is the original resistance before thetemperature is increased (i.e., R at T_(o)), and ΔR is the change inresistance brought on by change in temperature. The α for the RTD is0.00169° C.⁻¹, which is in good agreement with standard temperaturecoefficient of resistance for gold, which is 0.0034° C.⁻¹. NextApplicant performed the temperature measurement on a human forearm byusing epidermal RTD 225, along with the same thermal couple forreference. At the beginning the temperature of the skin is stabilized at30 degree C. and at around 100^(th) second and 180^(th) second an icebag is brought around the skin (where the sensors are mounted) and thentaken away, respectively. The results indicate that epidermal RTD 225successfully indicates (as well as the thermocouple) the change of thetemperature (i.e., that the skin temperature drops when the ice bag isapplied and skin temperature recovers when the ice bag is withdrawn). Inaddition, epidermal RTD 225 is much more compliant than the thermalcouple, which has a polyimide encapsulated rigid sensor as the probingtip.

For skin hydration monitoring, the hydration sensor (H sensor) 226 isfabricated on the ESS by the aforementioned cut-and-paste process.Sensor 226 was operated by measuring hydration with a moisture meter(e.g., MositureMeterSC Compact, Del fin Inc.), which is utilized for acalibration curve converting impedance to hydration level. Hydrationsensor 225 in ESS patch 200 measured the impedance continuously, and wasremoved for reference hydration level measurement by the moisture meter(e.g., 3 sec on skin and 2 minutes and 50 seconds between differentconditions). However, two different kinds of noise mode, “contacteffect” and “sweat effect”, were observed during the experiments, andlead to unreliable results. Still, correct curves of measurement wereachieved after the influence of contact effect and sweat effect wereeliminated. The results show the impedance measured by hydration sensoras function of frequency in different hydration levels from 32 to 90 byapplying body lotion on skin. The impedance decreases with increasingfrequency due to reduction of the imaginary part of impedance. Also, theimpedance decreases with increasing hydration level since thepermittivity and conductivity of skin increased.

Impedance as a function of hydration levels at different measuringfrequencies from 10 kHz to 100 kHz were also determined. As frequencyincreases, the impedance decreases since the imaginary part (capacitancepart) of the impedance decreases. Comparing the reduction of impedancemagnitude between at 10 kHz and 100 kHz, there is 87% and 85%,respectively. It represents that sensitivity is higher in 10 kHz than in100 kHz. Based on the above, trials were executed at a fixed frequencyof 10 kHz showing that as hydration level increases, the impedancemagnitude is reduced.

Applicant performed real-time skin hydration monitoring on the humanbody using sensors 225 on ESS patch 200. In order to demonstrate thehydration level variation within the volunteer subject, an “espressoscenario” was performed whereby the subject keeps calm from a startingpoint of measurement to 240 seconds, and then drinks a can of icedespresso. In the calm region, the hydration level slightly increasesfrom 69 to 83 and 78 to 90, as measured by sensor 225 and by the controlmeter, respectively. In contrast, the hydration level is elevatedsignificantly in the following 360 seconds (78 to 93 by sensor 225, and90 to 103 by the control meter). This may be due to the espresso causingbody sweating and elevating the hydration level. Interestingly, thehydration level drops gradually in the last 240 seconds due to the bodycooling down. During the whole period of measurement, the convertedresults of impedance measured by sensor 225 exhibits excellentconsistency corresponding to the results of the control meter.

Al-Coil-Based Wireless Strain Gauge

Deformation of the skin is captured by the wireless passive Al coil(227) surrounding the sensors and can be wirelessly transferred to areader via electromagnetic field (see FIG. 5(a)). This passive Al coilcan also be used as the NFC antenna for the EP, hydration andtemperature sensors in some cases, which ensures the potentialcapability of the wireless communication of the ESS patch. The resonantfrequency of an LRC circuit depends on its inductance and capacitance(see equation (1)). Miniaturized capacitors are low in cost and can beintegrated into small chips and easily plugged into most circuits.However, since the ESS structure needs to be planar, flexible, and thin,adding discrete capacitors involves connecting more components which canreduce robustness, increase cost, and increase the “real estate”footprint. To solve this issue, an embodiment has the resonant frequencylargely set by the inductor (as discussed above) so any change ininductance produces a large change in the frequency (which can then betranslated to change in temperature and the like). Inductance mostlydepends on the layout of the circuit in an embodiment (e.g., element 227of FIG. 2(a)). As discussed above, a planar circuit's inductance dependson the number of turns the strand takes, the shape of the turns, and thearea that is covered by the circuit.

In an embodiment, the passive wireless sensor 200 consists two layers ofAl-on-PET films in which the first layer forms the majority of theserpentine structures 225, 226, 227, 228 and the second layer forms thesmall bridge 253 that crosses over the first layer with its PET sidefacing the Aluminum side of the first layer. The Al-PET-Al structure atthe round pads 251, 252 form parallel plate capacitors connected inseries (in one embodiment the calculated capacitance is 3.76×10⁻¹² F.)and the serpentine wires act as both an inductor and a resistor, whichresults in a standard RLC circuit (see bottom panel of FIG. 5(a)). Sinceinductance largely depends on the number of turns of strands in sensor227, shape of the turns, and the area that is covered by the circuit, anembodiment has been formulated that shifts the resonant frequency of thecircuit by stretching or compressing or even bending sensor 227.

For example, in FIG. 5(a) a reader coil 528 was connected to anImpedance Analyzer via a BNC-RCA adaptor. The reader coil 528 wasinductively coupled to sensor 527 (analogous to coil 227), which acts asthe secondary coil in this transformer like setup (i.e., two coilsseparated from each other by a distance). The resonant frequency of thesensor 527 was obtained by measuring the impedance response of thecoupled circuit as a function of frequency. The resonant frequencycorresponds to a dip in the phase-frequency curve of the impedanceresponse. The trial setup is shown in FIG. 5(b).

Before making any measurement on the wireless sensor 527. Applicantmeasured the resonant frequency of the reader 528. Then Applicantperformed a stretching test of the coil (FIG. 5(c) and middle panel ofFIG. 5(a)) and resonant frequency of the reader at each applied strainwas recorded (FIG. 5(d)). FIG. 5(d) shows the resonant frequency of thecoil shifts from 38.6 MPa at 0% strain to 34.2 MPa at 27% strain.Notably, the ability of reading resonant frequency at 27.0% strainitself validates that the sensor stays integrated up to 27% strain.Resonant frequency as a function of applied strain is plotted as line529 in FIG. 5(e), which shows there is a monotonic negative relationshipbetween resonant frequency and applied strain. Details of the resonantfrequency corresponding to each applied strain can be found in thefollowing table:

Applied strain 0% 6.8% 13.5% 20.3% 27.0% RF(MPa) 38.6 36.6 35.4 34.334.2 Change in FR (%) 0 −5.18 −8.29 −11.14 −11.40

An explanation (proportional relation) for the negative monotonicrelationship between resonant frequency and the applied strain is thatstretching of the antenna 527 increases the area of the antenna, whichincreases the inductance and thus reduces the resonant frequency. Theinductance of a coil is approximately proportional to the square root ofthe area that is covered by the coil

L₀˜√{square root over (A)}˜√{square root over (l₁l₂)}  (4)

where l₁ and l₂ are the dimensions of the outer-most turns of the planarcoil in the longitudinal and transverse/horizontal directions.

For stretching (where ν is Poisson's ratio of the material):

l _(1(ε)) =l ₁×(1+ε),l _(2(ε)) =l ₂×(1−νε)   (5)

Then:

$\begin{matrix}{L_{(ɛ)} \sim \sqrt{\Lambda_{(ɛ)}} \sim \sqrt{{\Lambda \left( {1 + ɛ} \right)}\left( {1 - {v\; ɛ}} \right)} \sim {L_{0}\sqrt{\left( {1 + ɛ} \right)\left( {1 - {v\; ɛ}} \right)}}} & (6) \\{f_{(ɛ)} = {\frac{1}{2\pi \sqrt{L_{(ɛ)}C}} \sim {f_{0}\frac{1}{{{\left( {1 + ɛ} \right)\left( {1 - {v\; ɛ}} \right)}}^{0.25}}} \sim {f_{0}\left( {1 + {\frac{1}{4}\left( {v - 1} \right)ɛ}} \right)}}} & (7)\end{matrix}$

where a character with a subscript “ε” denotes the characteristic whenstretched and a subscript “0” denotes that characteristic beforestretching. The “˜” symbol in equations (6) and (7) denotes“proportional”.

Planar rectangular inductor theory predicts inductance of the circuit indifferent applied strains. In this theory geometry of the rectangularcircuit with straight lines is used to calculate the self-inductance andmutual-inductance in an iterative manner and ultimate inductance is thesummation of all the self-inductance (L_(o)) and mutual-inductance (M).

L=ΣL _(o) +ΣM   (8)

The predicted result by using both of the theories are plotted in FIG.5(c) (see lines corresponding to Equations 7 and 8). The theoreticalresult and experimental result exhibit excellent agreement in predictingthe trend of resonant frequency as a function of the applied strain.

The effect of the distance (coupling factor k) between reader coil 528and sensor coil 527 was tested and shows the resonant frequency of thecoil 527 is almost independent of the distance between the coils whereasthe phase is not. Specifically, the closer the reader is to the coil,the larger the phase is deviated from 90 degrees, which is the phase ofthe reader only (i.e., before one puts the reader 528 close to thereader), thus the higher Q factor.

In FIG. 5(f), an on skin deformation measurement was performed byplacing the passive wireless coil sensor 527 on the outer side of thewrist and putting the wrist with the coil close to the reader 528. Threelayers of tattoo adhesive film were applied between the coil sensor andthe skin to enhance the adhesion. Applicant performed three positions ofthe hand, which are “flat”, “stretch” and “compress”, as shown in FIG.5(f). For the “flat” position the subject held his hand so the hand andarm formed a straight line. For the “stretch” position the hand was bentdownwards to an extreme position so the coil sensor 527 is fullystretched. For the “compress” stage the hand was bent upwards to anextreme position so the coil sensor is fully compressed. Results of theresonant frequency in the three positions are plotted in FIG. 5(g),which reveals several interesting phenomena. First, the resonantfrequency drops from 38.6 MPa to 13.92 MPa when coil 527 is applied onthe skin. This is due to the loading of the skin. The second observationis that “stretch” reduces the resonant frequency (from 13.92 MPa to12.99 MPa, −6.69% in change) whereas “compress” slightly increasesresonant frequency (from 13.92 MPa to 14.41 MPa, 3.52% in change).Different from the stretch test, resonant frequency change in the onskin test is due to the combination of the deformation of the coil 527as well as the change of the relative position to the reader 528. Thereason why the phase of resonant frequency for position “stretch”increases is because when the hand is bent away from the reader, theeffective distance of the reader to the coil increases and the longerdistance results in a shallower dip in the frequency sweeping curve.Repeatability tests were conducted by repeating the hand positionsequence (“flat” then “stretch” then “compress”) twice, which showed theinitial results were repeatable.

In an embodiment the passive Al coil 527 may transfer the local signalof the ECG sensors 228 wirelessly to a remote receiver (see FIG. 7 foran example of a remote receiver) via coil 528, which is extremely usefulfor noncontact diagnostics. In order to transfer the data properly, anembodiment ensures the resonant frequency does not change significantlyduring the transferring process. Applicant placed the Al coil 527 on thechest of the subject and a resonant frequency result was obtained whenthe subject exhibited deep inhalation and exhalation and showed that theresonant frequency changes from 13.06 MPa to 12.80 MPa (i.e., 1.99% inchange) for both of the deep inhalation and exhalation. However, thecurve for inhalation is more severely sloped than that of the exhalationwhich is due to the fact that when the subject breathes in the chestmoves towards the reader whereas when the subject breathes out the chestmoves away from the reader. The insensitivity of resonant frequency toinhalation and exhalation (which can be accommodated) makes it possiblefor the coil to be used in an antenna application.

Thus, coil 527 may intentionally exhibit a shift in the resonantfrequency under stretch and may be used to measure stretch in someapplications (e.g., bending a limb like that shown in FIG. 5(f)).However, instead of or in addition to being used as a strain gauge, 227can also potentially be designed as wireless antenna to transmit data.For example, in a situation where less flexing/stretching occursfunctioning as an antenna may be ideal. Such a situation may occur withsystem 200 on the chest used to record EP signals via sensors 228 andthen transmit that data via antenna/coil 227. While coupling betweenelements 228 and 227 is not shown in FIG. 2(a) such coupling could beperformed by a person having ordinary skill in the art. The transmitteddata could be processed using a system such as the system of FIG. 7.

FIG. 8 depicts a process stage in an embodiment of the invention. FIG. 8assumes process steps from FIGS. 2(a)-(c) have occurred producing skintape 141 coupled to strands 125, 126 but having TRT layers 103, 104removed. FIG. 8 further assumes the process steps from FIGS. 2(a)-(c)have occurred a second time, however in this case the PET/Au 101, 102combination from FIG. 2(a) is replaced with an Al/PET element that has“flipped” in relation to the PET/Au orientation. As a result Al strands109, 110 are now in contact with tape 141 and PET 101 is further awayfrom tape 141. In FIG. 8 TRT layers 103′, 104′ (analogous to layers 103,104 from FIG. 1(a)) are still contacting strands 191, 192. However, aswas the case in FIG. 1(f), TRT layers 103′, 104′ will be removed andreplaced with liner 142, which will then cover, directly or indirectly,each of strands 191, 192, 125, 126. Notably, in an embodiment aluminumelements 109, 110 have a height 193 greater than a height 194 for Auelements 125, 126. Further, strands 191, 192 have height 195 greaterthan a height 196 for strands 125, 126.

Thus, FIG. 8 addresses an alternative embodiment whereby two independenttransfers (first Au patterns and then Al patterns or vice versa) occur,with the “longhorn” patterns (see FIG. 2(a)) as the alignment markers sothe relative position between the Au and Al patterns can be achieved asdesigned. The use of different materials within a single ESS allows fora thick metal to be used for the antenna 227 (while a thin metal is usedfor other sensors like sensor 228). The thick metal offers lowerresistance than the thin strands used for sensor 228 and the like. Thelower resistance reduces antenna loss. Al is used because in thequantities needed for the thickened strand Au may be cost prohibitive.

While FIG. 8 implies “two passes” to include an Al layer and an Aulayer, the process may repeat to add still additional layers and/ormaterials. Also, the use of the term “layer” here does not diminish thefact that in an embodiment both Au and Al both directly contact asubstrate, such as skin tape 141. Note the thickness increase for the Alis gained by increasing its height 193 (versus height 194). The width197 of the Al strands is equal to the width 198 of the Au strands inthis embodiment. This promotes flexibility or stretch for the Al strands(whereas making the Al strands with a wider width 197 may lead togreater failure rates under typical stresses experienced by ESS).Furthermore, increasing width 197 would consume valuable real estate onthe ESS, thereby reducing room for other sensors in a multiparametricESS (where real estate is at a premium). In an embodiment, the heights190, 199 for PFT components of the strands may be equal or unequal toeach other. In an embodiment, the widths (197, 198) for PFT componentsof the strands may be equal or unequal to each other. Further, the “flipflopping” of the Al/PET and PET/Au helps keep the Au in direct contactwith the skin (once any liner is removed and the ESS is applied to thepatient) and the Al not in contact with the skin (to promotebiocompatibility concerns whereby exposure of skin to Al may beundesirable).

FIG. 10 includes process 900′ with elements 901′ (“Conduct elements 905,910, 915, 920, 925, 930, 935 from FIG. 9 using first material (e.g., Au)for first conductive element”); 905′ (“Provide second conductive elementusing second material (e.g., metal such Al or semiconductor element suchas Si) for second conductive element, on additional first substrate(e.g., polymer such as PFT)”); 910′ (“Bond additional first substrate toadditional second substrate (e.g., TRT) to form a second composite andcouple additional second substrate to manufacturing platform/additionalmanufacturing platform (e.g., cutting pad)”); 915′ (“Position secondcomposite in forming tool/additional forming tool (e.g., knife or laserbased construction tool configured to form strands from secondconductive element)” which may necessarily include multiple substrates(e.g., “additional first substrate” and “additional second substrate”)in the forming tool/additional forming tool); 920′ (“Form patterns(e.g., strands) in second conductive element”); 925′ (“Expose secondcomposite to heat”); 930′ (“Remove unwanted second conductive elementportions from second composite”); 935′ (“Couple second composite tothird substrate (e.g., skin tape), in location between or adjacent tofirst composite located on third substrate, and remove additional secondsubstrate”); 940′ (“Couple second composite to fourth substrate (e.g.,liner to keep Au and Al strands from premature exposure”); 945′(“Position multiple ESS on continuous deployment system (e.g., largeroll of ESS whereby perforations allow ESS to be removed from deploymentsystem one by one)”).

Respiration Rate Measurement

Unlike conventional micro fabrication techniques, the cut and pasteapproach can be applied to a much broader category of materials.Applicant fabricated a functional stretchable strain gauge system, whichincludes electrically conductive rubber (ECR; Elastosil® LR 3162, WackerSilicones) as the resistor component and 100 nm gold serpentine wire asthe stretchable interconnect, by exploiting an embodiment of the cut andpaste method.

Three types of strain gauges are fabricated as shown in FIG. 6(a). Thelongitudinal strain gauge 601 and transverse strain gauge 602 are usedto measure the strain corresponding to longitudinal and transversedirections by measuring the change in resistance in the gauges. TheWheatstone bridge based gauge 603 is used to measure thetemperature-effect-free strain by measuring the voltage in the gauge. Aproperty of a strain gauge is its Gauge Factor (GF), which is defined asthe ratio of the fractional resistance change (ΔR/R₀) to the appliedstrain (ε):

$\begin{matrix}{{GF} = \frac{\Delta \; R\text{/}R_{0}}{ɛ}} & (9)\end{matrix}$

The GF of 601 and 602 are measured with tensile strain applied along thevertical direction and the results are plotted in FIG. 6(b). The GF of601 is 5.4 and the GF of 602 is −2.7 as it is subjected to horizontalcompressive strain due to Poisson's effect of the Tegaderm™ substrate.

In an embodiment design of the strain gauge system follows a basicprinciple of skin-mountable strain gauges where the idea is to configurethe system by using different in-plane geometry and different materialsso the overall resistance change of the system approaches the localresistance change of the resistors.

For increased accuracy, Wheatstone bridge 603 is adopted to eliminatethe temperature effect. Input voltage is applied across two diagonalvertices of the bridge and output voltage is measured across the othertwo diagonal vertices. The result of the fractional voltage change as afunction of strain is plotted in FIG. 6(c). This shows the curve islinear up to 5% strain and the slope, which is a GF-like parameter forthe Wheatstone bridge equal to 20.2. FEM results are in FIG. 6(d) andshow the longitudinal resistor properly accommodates the longitudinalstrain and the transverse resistor takes care of the transverse strain.

FIGS. 6(e)-(h) illustrate an on skin test performed by applying thestrain gauges of FIG. 6(a) on the chest of the subject during variousrespirational patterns. FIG. 6(f) shows the real time measurement of theresistive result for normal respiration rate by using a longitudinalresistor 601. The respiratory rate of the male subject is measured to be6 inhalation-exhalation cycles in 20 seconds, which exhibits goodconsistency with the normal statistic respiratory rate of 16 to 20 timesper minute. FIGS. 6(g)-(h) respectively show three different respirationpatterns measured in real-time, including quiet breathing, deepbreathing, and coughing. The figures show deep breathing induces moreintense voltage change than quiet breathing, which means the chest movesmore for deep breathing than quiet breathing. Also, the respiratoryfrequency for deep breathing is smaller than that of quiet breathing. Tobe specific, in deep breathing the subject takes about 2 seconds forinhalation and 3 seconds for exhalation, which is much longer that thanthat of the quiet breathing. Respiration rate for coughing is alsocaptured by the Wheatstone bridge, with repeated patterns due tomultiple coughs shown in FIG. 6(h).

ESS discussed herein may utilize a system such as the system of FIG. 7,discussed below. For example, EP signals from sensors 228 may be wiredto a node such as node 1000 (via direct wiring contacting pads 228′)whereby node 1000 processes and displays the signals and performsmeasurements (e.g., R-R intervals). However, in other embodiments thesignals may communicated via wireless means using antenna 227.Embodiments may be used in many different types of systems. For example,in one embodiment a communication device (e.g., Smartphone) can bearranged to perform the various methods and techniques described herein.Of course, the scope of the present invention is not limited to acommunication device, and instead other embodiments can be directed toother types of apparatus for processing instructions.

Program instructions may be used to cause a general-purpose orspecial-purpose processing system that is programmed with theinstructions to perform the operations described herein. Theseinstructions may be used to process signals (e.g., EP signals) orprogram a machine to cut or otherwise form (e.g., via knife or laser)strands for an ESS. Alternatively, the operations may be performed byspecific hardware components that contain hardwired logic for performingthe operations, or by any combination of programmed computer componentsand custom hardware components. The methods described herein may beprovided as (a) a computer program product that may include one or moremachine readable media having stored thereon instructions that may beused to program a processing system or other electronic device toperform the methods or (b) at least one storage medium havinginstructions stored thereon for causing a system to perform the methods.The term “machine readable medium” or “storage medium” used herein shallinclude any medium that is capable of storing or encoding a sequence ofinstructions (transitory media, including signals, or non-transitorymedia) for execution by the machine and that cause the machine toperform any one of the methods described herein. The term “machinereadable medium” or “storage medium” shall accordingly include, but notbe limited to, memories such as solid-state memories, optical andmagnetic disks, read-only memory (ROM), programmable ROM (PROM),erasable PROM (EPROM), electrically EPROM (EEPROM), a disk drive, afloppy disk, a compact disk ROM (CD-ROM), a digital versatile disk(DVD), flash memory, a magneto-optical disk, as well as more exoticmediums such as machine-accessible biological state preserving or signalpreserving storage. The medium may be on an ESS or coupled thereto viadirect or indirect means. A medium may include any mechanism forstoring, transmitting, or receiving information in a form readable by amachine, and the medium may include a medium through which the programcode may pass, such as antennas, optical fibers, communicationsinterfaces, etc. Program code may be transmitted in the form of packets,serial data, parallel data, etc., and may be used in a compressed orencrypted format. Furthermore, it is common in the art to speak ofsoftware, in one form or another (e.g., program, procedure, process,application, module, logic, and so on) as taking an action or causing aresult. Such expressions are merely a shorthand way of stating that theexecution of the software by a processing system causes the processor toperform an action or produce a result.

Referring now to FIG. 7, shown is a block diagram of a system embodiment1000 in accordance with an embodiment of the present invention. System1000 may be included in, for example, a mobile computing node such as acellular phone, smartphone, tablet, Ultrabook®, notebook, laptop,personal digital assistant, and mobile processor based platform.

Shown is a multiprocessor system 1000 that includes a first processingelement 1070 and a second processing element 1080. While two processingelements 1070 and 1080 are shown, it is to be understood that anembodiment of system 1000 may also include only one such processingelement. System 1000 is illustrated as a point-to-point interconnectsystem, wherein the first processing element 1070 and second processingelement 1080 are coupled via a point-to-point interconnect 1050. Itshould be understood that any or all of the interconnects illustratedmay be implemented as a multi-drop bus rather than point-to-pointinterconnect. As shown, each of processing elements 1070 and 1080 may bemulticore processors, including first and second processor cores (i.e.,processor cores 1074 a and 1074 b and processor cores 1084 a and 1084b). Such cores 1074, 1074 b, 1084 a, 1084 b may be configured to executeinstruction code in a manner similar to methods discussed herein.

Each processing element 1070, 1080 may include at least one sharedcache. The shared cache may store data (e.g., instructions) that areutilized by one or more components of the processor, such as the cores1074 a, 1074 b and 1084 a, 1084 b, respectively. For example, the sharedcache may locally cache data stored in a memory 1032, 1034 for fasteraccess by components of the processor. In one or more embodiments, theshared cache may include one or more mid-level caches, such as level 2(L2), level 3 (L3), level 4 (L4), or other levels of cache, a last levelcache (LLC), and/or combinations thereof.

While shown with only two processing elements 1070, 1080, it is to beunderstood that the scope of the present invention is not so limited. Inother embodiments, one or more additional processing elements may bepresent in a given processor. Alternatively, one or more of processingelements 1070, 1080 may be an element other than a processor, such as anaccelerator or a field programmable gate array. For example, additionalprocessing element(s) may include additional processors(s) that are thesame as a first processor 1070, additional processor(s) that areheterogeneous or asymmetric to first processor 1070, accelerators (suchas, e.g., graphics accelerators or digital signal processing (DSP)units), field programmable gate arrays, or any other processing element.There can be a variety of differences between the processing elements1070, 1080 in terms of a spectrum of metrics of merit includingarchitectural, microarchitectural, thermal, power consumptioncharacteristics, and the like. These differences may effectivelymanifest themselves as asymmetry and heterogeneity amongst theprocessing elements 1070, 1080. For at least one embodiment, the variousprocessing elements 1070, 1080 may reside in the same die package.

First processing element 1070 may further include memory controllerlogic (MC) 1072 and point-to-point (P-P) interfaces 1076 and 1078.Similarly, second processing element 1080 may include a MC 1082 and P-Pinterfaces 1086 and 1088. MC's 1072 and 1082 couple the processors torespective memories, namely a memory 1032 and a memory 1034, which maybe portions of main memory locally attached to the respectiveprocessors. While MC logic 1072 and 1082 is illustrated as integratedinto the processing elements 1070. 1080, for alternative embodiments theMC logic may be discreet logic outside the processing elements 1070,1080 rather than integrated therein.

First processing element 1070 and second processing element 1080 may becoupled to an I/O subsystem 1090 via P-P interfaces 1076, 1086 via P-Pinterconnects 1062, 10104, respectively. As shown. I/O subsystem 1090includes P-P interfaces 1094 and 1098. Furthermore, I/O subsystem 1090includes an interface 1092 to couple I/O subsystem 1090 with a highperformance graphics engine 1038. In one embodiment, a bus may be usedto couple graphics engine 1038 to I/O subsystem 1090. Alternately, apoint-to-point interconnect 1039 may couple these components.

In turn, I/O subsystem 1090 may be coupled to a first bus 10110 via aninterface 1096. In one embodiment, first bus 10110 may be a PeripheralComponent Interconnect (PCI) bus, or a bus such as a PCI Express bus oranother third generation I/O interconnect bus, although the scope of thepresent invention is not so limited.

As shown, various I/O devices 1014, 1024 may be coupled to first bus10110, along with a bus bridge 1018 which may couple first bus 10110 toa second bus 1020. In one embodiment, second bus 1020 may be a low pincount (LPC) bus. Various devices may be coupled to second bus 1020including, for example, a keyboard/mouse 1022, communication device(s)1026 (which may in turn be in communication with a computer network),and a data storage unit 1028 such as a disk drive or other mass storagedevice which may include code 1030, in one embodiment. The code 1030 mayinclude instructions for performing embodiments of one or more of themethods described above. Further, an audio I/O 1024 may be coupled tosecond bus 1020.

Note that other embodiments are contemplated. For example, instead ofthe point-to-point architecture shown, a system may implement amulti-drop bus or another such communication topology. Also, theelements of FIG. 7 may alternatively be partitioned using more or fewerintegrated chips than shown in the FIG. 7.

The following examples pertain to further embodiments.

Example 1 includes a sensor system comprising: a first epidermal sensorsystem (ESS) comprising: a first substrate; a first strand including afirst polymer directly contacting the first substrate and a first metaldirectly contacting the first polymer; an additional first strandincluding an additional first polymer directly contacting the firstsubstrate and an additional first metal directly contacting theadditional first polymer; and a first protective substrate on the firstmetal and the additional first metal.

For example, the substrate may include skin tape or tattoo paper.

In example 2 the subject matter of Example 1 can optionally include,wherein the first strand includes a first portion and the additionalfirst stand includes an additional first portion that is parallel to thefirst portion.

For example, portions 261, 262 have areas where both are moving towardsthe center of ESS 200 and are parallel to each other.

In example 3 the subject matter of the Examples 1-2 can optionallyinclude wherein the first strand directly contacts the additional firststrand.

For example, at location 289, strand pair 265, 266 has a transition fromstrand 265 to strand 266 where the two strands directly contact eachother.

In example 4 the subject matter of Examples 1-3 can optionally include asecond ESS comprising: a second substrate; a second strand including asecond polymer directly contacting the second substrate and a secondmetal directly contacting the second polymer; an additional secondstrand including an additional second polymer directly contacting thesecond substrate and an additional second metal directly contacting theadditional second polymer; and a second protective substrate on thesecond metal and the additional second metal; wherein the first andsecond ESSs are adjacent one another on a roll of three or more ESSsthat progressively encircle a middle portion of the roll.

Thus, an embodiment allows for a roll of ESSs that can be unrolled oneESS at the time. Other systems may deploy a strip of ESSs including fouror five ESSs on the single strip all co-linear with each other. Someembodiments may include a rectangular sheet having three rows of ESSswith each row including three to four ESSs.

In example 5 the subject matter of the Examples 1-4 can optionallyinclude wherein the first and second substrates each include skin tapeportions that are monolithic with each other, the first and secondpolymers each include polyethylene terephthalate (PET), the first andsecond metals each include gold, and the first and second protectivesubstrates each include a liner.

However, in other embodiments the first and second substrates eachinclude tattoo paper portions that are monolithic with each other.

Thus, an embodiment may provide a continuous strip of tape that extendsalong a roll of ESSs, whereby the tape has perforations or other areasthat lack structural integrity such that a user can simply remove oneESS from another ESS. An embodiment may provide a continuous monolithicliner that extends along a roll of ESSs, whereby the liner hasperforations or other areas that lack structural integrity such that auser can simply remove one ESS from another ESS. An embodiment mayinclude continuous skin tape and liner that extend across multiple ESSs,such as a roll or sheet of ESSs.

In example 6 the subject matter of the Examples 1-5 can optionallyinclude wherein the first and second protective substrates aremonolithic with one another and include a perforated scam between thefirst and second protective substrates.

In example 7 the subject matter of the Examples 1-6 can optionallyinclude wherein the first ESS comprises: a third strand including athird metal, directly contacting the first substrate, and a thirdpolymer; and an additional third strand including an additional thirdmetal, directly contacting the first substrate, and an additional thirdpolymer; wherein the first protective substrate is on the third metaland the additional third metal; wherein the first metal includes a firstmaterial different from a third material included in the third metal.

In an embodiment, the first and second metals include Au and the thirdmetal includes Al. Of course, other conductive materials may be usedincluding Cu, Si, SiGe, and the like.

In example 8 the subject matter of the Examples 1-7 can optionallyinclude wherein the first ESS comprises: a second strand including asecond metal, directly contacting the first substrate, and a secondpolymer; and an additional second strand including an additional secondmetal, directly contacting the first substrate, and an additional secondpolymer; wherein the first protective substrate is on the second metaland the additional second metal; wherein the first metal includes afirst material different from a second material included in the secondmetal.

In example 9 the subject matter of the Examples 1-8 can optionallyinclude wherein (a) the first substrate includes a long axis in ahorizontal plane, (b) the first metal includes a first height orthogonalto the horizontal plane, (c) the second metal includes a second heightorthogonal to the horizontal plane, and (d) the second height is greaterthan the first height.

In example 10 the subject matter of the Examples 1-9 can optionallyinclude wherein (a) the first metal includes a first width parallel tothe horizontal plane, (b) the second metal includes a second widthparallel to the horizontal plane, and (d) the second width equals thefirst width.

In example 11 the subject matter of the Examples 1-10 can optionallyinclude wherein the first material includes gold and the second materialincludes aluminum.

In example 12 the subject matter of the Examples 1-11 can optionallyinclude wherein the second strand and the additional second strand areformed in complementary serpentine patterns; wherein the second strandincludes a maximum radius of curvature directly adjacent where theadditional second strand includes a minimum radius of curvature; whereinthe second strand includes a minimum radius of curvature directlyadjacent where the additional second strand includes a maximum radius ofcurvature.

For example, in FIG. 3 a minimum radius of curvature 389 aligns with amaximum radius of curvature 399 for complementary serpentine pattern390.

In example 13 the subject matter of the Examples 1-12 can optionallyinclude wherein the second material includes aluminum and the secondstrand and the additional second strand are each included in a straingauge and an antenna.

In example 14 the subject matter of the Examples 1-13 can optionallyinclude including a second coil configured to communicate with theantenna via inductive coupling.

For example, coil 528 may be included in a kit with several ESS.

In example 15 the subject matter of the Examples 1-14 can optionallyinclude wherein the first protective substrate directly contacts thefirst metal and the additional first metal.

In example 16 the subject matter of the Examples 1-15 can optionallyinclude wherein the first strand intersects the additional first standat a first intersection; wherein the first strand includes a minimumdiameter at the intersection and widens as the first strand moves awayfrom the intersection.

For example, FIGS. 4(a)-(l) show images of various embodiments. FIGS.4(a), (b), and (c), show a new, used, and damaged blade, respectively.Cutting results with different combinations of selected cuttingparameters in the Cameo® cutting machine software (where KT stands forKapton thickness, Sh for sharpness, Ra for cutting rate, Th forthickness, NB for new blade, UB for used blade) are given as follows:FIG. 4(d) KT=25.4 μm, Sh=5, Ra=1, Th=7, NIB, FIG. 4(e) KT=25.4 μm,Sh=10, Ra=1, Th=7, NB, FIG. 4(f) KT=25.4 μm, Sh=5, Ra=10, Th=7, NB, FIG.4(g) KT=25.4 μm, Sh=5, Ra=1, Th=20 NB, FIG. 4(h) KT=12.7 μm, Sh=5, Ra=1,Th=7, NB, FIG. 4(i) KT=25.4 μm, Sh=10, Ra=1, Th=7, UB. A minimumdiameter is shown at 372, 371 where clearly the portions then broaden at362, 361. Portions 372, 373, 371 indicate areas where a knife bladestopped and pivoted or otherwise shifted causing an overcut not presentin lithography based epidermal sensors. FIGS. 4(j)(k)(l) show differentintersections.

Example 17 includes a method comprising: providing a first conductiveelement on a first substrate; coupling the first conductive element to asecond substrate to form a composite; coupling the second substrate to amanufacturing platform; positioning the composite in a forming toolincludes a member selected from the group comprising a knife and alaser; forming patterns in the first conductive element; exposing thecomposite to heat; removing unwanted first conductive element portionsfrom the composite; and coupling the composite to a third substrate andremove the second substrate.

In an embodiment a manufacturing platform may include a table, cuttingpad, glass plane, ceramic plane, and the like. In an embodiment aconductive element may include a metal (Al, Cu, Au), a conductive purepolymer or polymer composite, and the like.

In example 18 the subject matter of example 17 can optionally includecomprising positioning a first epidermal sensor system (ESS) includingthe first conductive element adjacent a second ESS on a roll of three ormore ESSs that progressively encircle a middle portion of the roll.

Example 19 includes a sensor system comprising: a first epidermal sensorsystem (ESS) comprising: a first substrate; a first strand including afirst polymer coupled to the first substrate and a first metal coupledto the first polymer; an additional first strand including an additionalfirst polymer coupled to the first substrate and an additional firstmetal coupled to the additional first polymer; and a first protectivesubstrate on the first metal and the additional first metal.

Thus, in embodiment the first polymer need not directly contact thefirst substrate but may instead do so indirectly.

In example 20 the subject matter of Example 19 can optionally includewherein the first ESS comprises: a second strand including a secondmetal, coupled to the first substrate, and a second polymer; and anadditional second strand including an additional second metal, coupledto the first substrate, and an additional second polymer; wherein thefirst protective substrate is on the second metal and the additionalsecond metal; wherein the first metal includes a first materialdifferent from a second material included in the second metal.

Example 21 includes a sensor system comprising: a first epidermal sensorsystem (ESS) comprising: a first substrate; a first strand including afirst polymer coupled to the first substrate and a first conductiveelement coupled to the first polymer; an additional first strandincluding an additional first polymer coupled to the first substrate andan additional first conductive element coupled to the additional firstpolymer; and a first protective substrate on the first conductiveelement and the additional first conductive element.

In example 22 the subject matter of Example 21 can optionally includewherein the first ESS comprises: a second strand including a secondconductive element, coupled to the first substrate, and a secondpolymer; and an additional second strand including an additional secondconductive element, coupled to the first substrate, and an additionalsecond polymer; wherein the first protective substrate is on the secondconductive element and the additional second conductive element; whereinthe first conductive element includes a first material different from asecond material included in the second conductive element.

The foregoing description of the embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formsdisclosed. This description and the claims following include terms, suchas left, right, top, bottom, over, under, upper, lower, first, second,etc. that are used for descriptive purposes only and are not to beconstrued as limiting. For example, terms designating relative verticalposition refer to a situation where a device side (or active surface) ofa substrate or integrated circuit is the “top” surface of thatsubstrate; the substrate may actually be in any orientation so that a“top” side of a substrate may be lower than the “bottom” side in astandard terrestrial frame of reference and still fall within themeaning of the term “top.” The term “on” as used herein (including inthe claims) does not indicate that a first layer “on” a second layer isdirectly on and in immediate contact with the second layer unless suchis specifically stated; there may be a third layer or other structurebetween the first layer and the second layer on the first layer. Theembodiments of a device or article described herein can be manufactured,used, or shipped in a number of positions and orientations. Personsskilled in the relevant art can appreciate that many modifications andvariations are possible in light of the above teaching. Persons skilledin the art will recognize various equivalent combinations andsubstitutions for various components shown in the Figures. It istherefore intended that the scope of the invention be limited not bythis detailed description, but rather by the claims appended hereto.

1. A sensor system comprising: a first epidermal sensor system (ESS)comprising: a first substrate; a first strand including a first polymerdirectly contacting the first substrate and a first metal directlycontacting the first polymer; an additional first strand including anadditional first polymer directly contacting the first substrate and anadditional first metal directly contacting the additional first polymer;and a first protective substrate on the first metal and the additionalfirst metal.
 2. The system of claim 1, wherein the first strand includesa first portion and the additional first stand includes an additionalfirst portion that is parallel to the first portion.
 3. The system ofclaim 2, wherein the first strand directly contacts the additional firststrand.
 4. The system of claim 1 comprising: a second ESS comprising: asecond substrate; a second strand including a second polymer directlycontacting the second substrate and a second metal directly contactingthe second polymer; an additional second strand including an additionalsecond polymer directly contacting the second substrate and anadditional second metal directly contacting the additional secondpolymer; and a second protective substrate on the second metal and theadditional second metal; wherein the first and second ESSs are adjacentone another on a roll of three or more ESSs that progressively encirclea middle portion of the roll.
 5. The system of claim 4, wherein thefirst and second substrates each include skin tape portions that aremonolithic with each other, the first and second polymers each includepolyethylene terephthalate (PET), the first and second metals eachinclude gold, and the first and second protective substrates eachinclude a liner.
 6. The system of claim 5, wherein the first and secondprotective substrates are monolithic with one another and include aperforated seam between the first and second protective substrates. 7.The system of claim 4, wherein the first ESS comprises: a third strandincluding a third metal, directly contacting the first substrate, and athird polymer; and an additional third strand including an additionalthird metal, directly contacting the first substrate, and an additionalthird polymer; wherein the first protective substrate is on the thirdmetal and the additional third metal; wherein the first metal includes afirst material different from a third material included in the thirdmetal.
 8. The system of claim 1, wherein the first ESS comprises: asecond strand including a second metal, directly contacting the firstsubstrate, and a second polymer; and an additional second strandincluding an additional second metal, directly contacting the firstsubstrate, and an additional second polymer; wherein the firstprotective substrate is on the second metal and the additional secondmetal; wherein the first metal includes a first material different froma second material included in the second metal.
 9. The system of claim8, wherein (a) the first substrate includes a long axis in a horizontalplane, (b) the first metal includes a first height orthogonal to thehorizontal plane, (c) the second metal includes a second heightorthogonal to the horizontal plane, and (d) the second height is greaterthan the first height.
 10. The system of claim 9, wherein (a) the firstmetal includes a first width parallel to the horizontal plane, (b) thesecond metal includes a second width parallel to the horizontal plane,and (d) the second width equals the first width.
 11. The system of claim8, wherein the first material includes gold and the second materialincludes aluminum.
 12. The system of claim 8: wherein the second strandand the additional second strand are formed in complementary serpentinepatterns; wherein the second strand includes a maximum radius ofcurvature directly adjacent where the additional second strand includesa minimum radius of curvature; wherein the second strand includes aminimum radius of curvature directly adjacent where the additionalsecond strand includes a maximum radius of curvature.
 13. The system ofclaim 12, wherein the second material includes aluminum and the secondstrand and the additional second strand are each included in a straingauge and an antenna.
 14. The system of claim 13 including a second coilconfigured to communicate with the antenna via inductive coupling. 15.The system of claim 1, wherein the first protective substrate directlycontacts the first metal and the additional first metal.
 16. Thestructure of claim 1 wherein the first strand intersects the additionalfirst stand at a first intersection; wherein the first strand includes aminimum diameter at the intersection and widens as the first strandmoves away from the intersection. 17-18. (canceled)
 19. A sensor systemcomprising: a first epidermal sensor system (ESS) comprising: a firstsubstrate; a first strand including a first polymer coupled to the firstsubstrate and a first conductive element coupled to the first polymer;an additional first strand including an additional first polymer coupledto the first substrate and an additional first conductive elementcoupled to the additional first polymer; and a first protectivesubstrate on the first conductive element and the additional firstconductive element.
 20. The system of claim 19, wherein the first ESScomprises: a second strand including a second conductive element,coupled to the first substrate, and a second polymer; and an additionalsecond strand including an additional second conductive element, coupledto the first substrate, and an additional second polymer; wherein thefirst protective substrate is on the second conductive element and theadditional second conductive element; wherein the first conductiveelement includes a first material different from a second materialincluded in the second conductive element.